Process of making pressure sensitive record material



' on February 23, 1940.

Patented Nov. 18, 1952 PROCESS OF MAKING PRESSURE SENSITIVE RECORDMATERIAL Barrett K. Green, Dayton, Ohio, assignor to The National CashRegister Company, Dayton, Ohio, a corporation of Maryland No Drawing.Original application November 8,

1947, Serial No. 784,939. Divided and this application October 4, 1949,Serial No. 119,576

13 Claims.

This invention relates to improvements in process of making apressure-sensitive record material. This application is a division ofthe application of Barrett K. Green, Serial No. 78%,939, filed November8, 1947, for Process of Making Pressure Sensitive Record Material,

' which issued as U. S. Patent 2,505,471 on April The principal objectof this invention is to provide a process of making a pressure-sensitiverecord material, on which a mark of distinctive color may be produced bythe mere application of localized pressure, and which is not subject tothe disadvantages inherent in the pressure-sensitive record materialdisclosed in Uni-ted States Letters Patent No. 2,299,693, patentedOctober 20, 1942, on the application filed by Barrett K. Green Thatpatent discloses a pressure-sensitive record material including thecombination of an insulating medium, a rupturable solid material such asgum dammar, having included therein interspersed droplets of a pluralityof liquid reagents, which are chemically reactive to produce adistinctive color in the record material at the points of application oflocalized pressure thereto, such pressure rupturing the insulatingmedium to permit chemical reaction between the two liquid reagents. Thetwo reagents disclosed in that Patent 2,299,693 are gallic acid andferric ammonium sulphate, each dissolved in glycerine. These reagentsare ionized by the glycerine, which constitutes an ionizing medium, andthe chemical reaction proceeds by interchange of ions when the twosolutions are allowed to ruin, upon the rupture of the insulatingmedium. The reaction disclosed in that patent depends upon the presenceof the reagents in an ionizing medium. However, any available ionizingmedium is hygroscopic, with the result that the record material, made inac cordance with this patent, is sensitive to an excess of moisture, andconditions of high humidity may cause the insulating medium to cease tobe effective, with the result that the chemical reaction takes placewithout any application oi localized pressure, and the record materialis stained and discolored, so that it ceases to be useful.

As stated above, the principal object of the present invention is toprovide a process of making a pressure-sensitive record material that isnot subject to the defects and disadvantages of that disclosed in PatentNo. 2,299,693, as indicated above.

Another object of the present invention is to provide a process ofmaking a record material upon which a mark of distinctive color may beproduced, at the points of application of localized pressure thereto, bysuch mere application of localized pressure, and which will not becomediscolored or stained due to the effect of light, atmosphericconditions, or aging.

In short, it is the object of this invention to provide a process ofmaking a pressure-sensitive record material in which the mark ofdistinctive color will be produced only at the points'oi application oflocalized pressure, and at no other points, and under no otherconditions.

Another object of this invention is to'provide a process of making apressure-sensitive record material in which the mark of distinctivecolor is produced by the chemical reaction of color-forming reactants,in the absence of any liquid ionizillg' medium therefor.

A further object of this invention is to'provide a process of making apressure-sensitive record material in which a mark of distinctive coloris produced by a reaction between solid pa ti les of color-formingreactants.

Further ob ects, and objects relating to details and economies ofoperation, will definitely appear from the detailed description tofollow. The

. objects of this invention have been attained by the severalembodiments thereof described in de tail in the following specification.This invention is clearly defined and pointed out in the appendedclaims. I

In general, the present invention contemplates a process of making apressure-sensitive record material including the forming on a supportingmember a film-like deposit of solid particles of a plurality ofadsorption color-forming reactants disposed in interspersed contiguitywith each other, such reactants being so selected that they react, inthe absence of a liquid ionizing medium for the reactants, to form adistinctive color when brought into adsorption contact with each other,and a solid insulating medium insulating said reactants fromcolor-forming reaction contact with each other. Upon application oflocalized pressure to the record material, as by drawing a, stylusacross it, the insulating medium is ruptured at the points ofapplication of said localized pressure, and such rupture permitscolor-forming reaction contact between the reactants at such points, inthe absence of any liquid ionizing medium for said reactants. The resultis that a mark of distinctive color is produced by the mere applicationof localized pressure.

The color reaction employed is of the so-called, adsorption type whereinan inorganic compound causes a color change in an organic compoundcoming into adsorption contact therewith.

f the reactant materials employed,.the organic material is an electrondonor aromatic compound having a double bond system which is convertibleto a more highly polarized conjugated form upon taking part in anelectron acceptor-donor solid surface. chemical reaction, giving it adistinctive color, and the inorganic reactant is a material which is anacid relative to the organic material so as to be an electron acceptorwhen in adsorption contact therewith. Both materials are in fineparticle form in order to furnish a large reactant surface area per unitarea 'of the record material, which enhances the depth of color .perunit area of the record material.

vAccording to this invention, solid particles of a-plurality ofcolor-forming reactants are interspersedat random in va solid insulatingmedium, 'which insulates the particles from colorforming reactioncontact with each other. The rupture of thissoli'd insulating medium bythe application of localized pressure permits the solid particles ofcolor-forming reactants to react. with each other, at the points ofapplication of such pressure, to produce the mark of distinctive'color.According to another form of this invention, claimed in the applicationof which this is a division, solid particles of one of the colorformingreactants are carried by and dispersed in .a solid insulating medium, towhich a coating-of solid particles of another color-forming reactant isapplied. In this case, the application of localized pressure rupturesthe solid insulating medium, at the points of application of suchpressure, and brings about-color-forming reaction contact between thesolid part cles of colorforming reactants at such points, thu producingthe mark of distinctive color. Preferably, such pressure-sensitiverecord material includes a base web, such as a fibrous web of paper orthe like,

to'whic'h the coating of solid insulat ng medium and the color-formingreactants is applied.

Since it is difiicult to show precisely the spatial relationship betweenthe solid particles of coloriorming reactants, the solid insulatingmedium, and the baseweb, itis preferred not to attempt to illustrate.any embodiment of this invention by drawings.

The insulating medium is a pressure-rupturable film derived-from anorganic film-forming hydrophilie colloid substance.

Inthe following exam les, there will be described embodiments of thisinvention. by means ofwhich the ob ects of the invention have beensuccessfully attained.

The following embodiment of this invent on constitutes the best mode ofapplying the principle thereof contemplated up to the present time,andmav be considered the preferred embodiment.

- Itconsists of a process for making a pressuresensitive record materialthat comprises a base web, of paper or the like, to which is applied acoating including casein and solid particles of three color-formingreactants; namely, kaolin, the compound 3,3 bis (p-dimethylaminophenyl)-6 dimethylamino phthalide, referred to as crystal violet lactone andhaving the structure and the compound tetramethylbenzidine, having thestructure The casein constitutes the solid insulating medium, insulatingone of the color-forming reactants-that is, kaolin-from color-formingreaction contact with the other color-forming reactants-that is, crystalviolet lactone and tetramethylbenzidine. This record material is normanywhite or bluish white in color, and, upon the application of localizedpressure thereto, as by drawing a stylus thereover, a dark blue mark isproduced at the points of application of such localized pressure. Suchapplication of pressure ruptures the solid insulating medium at thepoints of application of pressure, permitting colorforming reactioncontact between the solid particles of kaolin and the solid particles ofcrystal violet lactone and tetramethylbenzidine, thus causing the colorchange at such points that produces the mark.

The compound 3,3 bis (p-dimethylaminophenyl)-6 dimethylaminophthalide-that is, crystal violet lactoneand the process of making itare disclosed in United State Letters Patent No. 2,417,897, issued March25, 1947, on the application of Clyde S. Adams filed June 16, 1945,although the compound is incorrectly named insaid patent as 3,3 bis(4-dimethylaminophenyl) -6 dimethylaminophenyl phthalide. Reissue PatentRe. 23,024 correctly names the compound.

It is not considered that the proportions, in which these severalingredients are present in the record material, are of particularimportance, but good results have been obtained with apressure-sensitive record material having such ingredients present inthe following proportions by weight in the coating on the base web:

Percent Casein -a 8.85 Kaolin -i 88.50 Crystal violet lactone 2.25Tetramethylbenzidine ..40

When these ingredients are applied to the paper as a coating thereon,such coating weighs about .0023 pound per square foot of surface and mayhave a thickness of the order of from .0005 to .091 inch. The thicknessof the coating varies, of course, with the treatment to which the recordmaterial is subjected in finishing. The solid particles of kaolin inthis record material may be of about the order of ten microns indiameter, although considerable variation in particle size is possiblewithout any ill effects. Particle 7 In another embodiment of thisinvention the compound 3,3 bis (p-dimethylaminophenyl) phthalide, alsoknown as malachite green lactcne, having the structure is used in :placeof the crystal violet lactone.

This record material is normally white or light in color, and, uponapplication of localized pressure thereto, as by drawing a stylusthereover, a mark of dark blue-green color is produced at the points ofapplication of such pressure.

It is understood that the process of making a pressure-sensitive recordmaterial described herein is susceptible of considerable variationwithout departing from the spirit of the invention;

What is claimed is:

1. The process of making a pressure-sensitive record material includingthe step of forming on a supporting member a film of a solid insulatingmedium, derived from an organic hydrophilic colloid substance, havinginterspersed therethrough at random solid particles or" a plurality ofadsorption color-forming reactants, disposed in contiguity, butinsulated from color-forming reaction contact by such medium, at leastone of said reactants being kaolin and at least another of saidreactants bein a mixture of the compound 3,3 bis(p-'dimethylaminophenyl) 6-dimethylami-no phthalide, having thestructure and the compound tetrarnethylbenzidine, having the structurenoon- O 0 the kaolin being in fine particle form providing a largeadsorbent surface area.

2. The process of claim 1, in which the solid insulating medium iscasein.

3. The process of making a pressure-sensitive record material includingthe step of forming on supporting member a film of casein havinginterspersed therethrough at random solid par ticies of a plurality ofadsorption color-forming reactants, disposed in contiguity, butinsulated from color-forming reaction contact by such casein film, atleast one of said reactants being an inorganic compound, and at leastanother of said reactants being an organic compound adsorbabletherewith, said reactants being so'selec'ted as to react in the absenceof an ionizing medium to form a distinctive color when brought intoadsorption contact with each other, the organic one of said reactantsbeing solid particles of an electron-donor aromatic organic compoundhaving a double bond system which is convertible to a more highlypolarized conjugated form upon taking part in an electron acceptor-donorsolid surface chemical reaction, giving it a distinctive color, and theinorganic reactant being in fine particle form providing a largeadsorbent surface area and which is an acid relative to the firstreactant so as to be an electron acceptor when in adsorption contactwith said first reactant.

i. The process of making a pressure-sensitive record material includingthe step of forming on a supporting member a film of solid insulatingmedium, derived from an organic hydrophilic colloid substance, havinginterspersed therethrough at random solid particles of a plurality ofadsorption color-forming reactants, disposed in contiguity but insulatedfrom color-forming reaction contact by such medium, at least one of saidreactants being an inorganic compound and another of said reactantsbeing the aromatic compound 3,3 bis(p-dimethylaminophenyl) -6-dimethylamino phthalide, having the structure I C=O said inorganiccompound being in fine particle form providing a large adsorbent surfacearea and which is an acid absorbent for said aromatic compound andacting as an electron acceptor when in adsorption contact therewith,whereby a distinctive col-or is formed in said aromatic compound on suchadsorption contact.

5. The process of claim 4 in which the 3,3 bis(p-dimethylaminophenyl) 6dimethylamino phthalide is mixed with the compoundtetramethylb-enzidine, having the structure 6. The process of making apressure-sensitive record material including the steps of forming adispersion of solid particles of a first colorforming reactant in asolution of casein, forming a dispersion of solid particles of a secondcolor-forming reactant in a solution of said casein, mixing saiddispersions, coating a base web with the mixture of said dispersions,and evaporating the solvent therefrom, leaving on the base web a coatingof solid casein having said solid reactant particles interspersedtherethrough at random, one of said reactants being an inorganiccompound and the other of said reactants being an organic compoundadsorbable therewith, and said reactants being so selected as to reactin the absence of an ionizing medium to form a distinctive color whenbrought into adsorption contact with each other, the organic reactantbeing an electron donor aromatic organic compound having a double bondsystem which is convertible to a more highly polarized conjugated formupon taking part in an electron acceptor-donor solid surface chemicalreaction, giving it a distinctive color, and the inorganic reactantbeing in fine particle form, providing a large adsorbent surface areaand which is an acid-relative to the organisms- -size of the crystalviolet lactone and the tetramethylbenzidine is largely determined by themethod of application of those ingredients. The particles of thesereactants may be as large as ten microns in diameter and frequently aremuch smaller.

Gelatin, methyl cellulose, starch, polyvinyl alcohol, and animal glueare representative organic hydrophilic colloid materials that may besubstituted for casein as the solid insulating medium. Any of thefollowing inorganic materials may be substituted for kaolin as one ofthe colorforming reactants: attapulgite (Attapulgus clay), pyrophyllite,talc, bentonite, halloysite, calcium sulphate, calcium citrate,magnesium trisilicate, zinc sulphide, zirconium dioxide, calciumphosphate, barium sulphate, and calcium fluoride. When any of thesematerials are substituted for the kaolin in this combination, theresulting record material will be white or bluish white in color, and adark blue mark will appear thereon as the result of the application oflocalized pressure.

If the tetramethylbenzidine be omitted and the pressure-sensitive recordmaterial be made using kaolin and crystal violet lactone as the solecolor-forming ingredients, the record material will be white in color,and application of localized pressure will produce a dark blue markthereon, but this mark may fade upon continued exposure to light underconditions of high humidity. On the other hand, if the crystal violetlactone be omitted and tetramethylbenzidine and kaolin be used as thesole color-forming reactants, the pressure-sensitive record materialproduced will be normally white, and application of localized pressurethereto will produce a green mark, which deepens in color upon aginganddoes not fade as readily as the mark produced by crystal violet lactoneand kaolin alone, under conditions of high humidity.

This pressure-sensitive record material is not substantially affected bythe amount of atmospheric humidity ordinarily encountered, although themark may fade somewhat if subjected to high humidity for along-continued period of time. However, this pressure-sensitive recordmaterial does not become stained or discolored by exposure to highhumidity for long periods of time, and retains its ability to respond tothe application of localized pressure, and to produce the mark ofdistinctive color, under such conditions. This is thought to be due tothe fact that the record material does not include any hygroscopicionizing media. Consequently, the structure of the record material isnot altered or modified due to the absorption of water from theatmosphere.

An embodiment of this invention successfully used for makingpressure-sensitive record material such as described above, using caseinas the solid insulating medium and kaolin, crystal violet lactone, andtetramethylbenzidine as the colorforming reactants, is as follows: 200grams of kaolin were made into a slurry with 20 grams of water, to which0.3% by weight of sodium metaphosphate was added as a dispersing agent.A casein solution was formed by dispersing 20 grams of casein in 139grams of cold water and stirring for fifteen minutes. This dispersion ofcasein in water was then heated to 60 degrees centigrade, and 5 grams ofcommercial 28% ammonium hydroxide solution were added and the solutionstirred for fifteen minutes while hot,

One-half of the casein solution thus formed was thoroughly mixed withthe kaolin slurry. 5.1 grams of crystal violet lactone and .9 gram oftetramethylbenzidine were then dissolved in 50 cc. of 3.7% hydrochloricacid solution, havin a specific gravity of 25 Be. at 20/4 centigrade. Tothe other half of the casein solution, 5 grams of commercial 28%ammonium hydroxide solution were added, and the acidified solution ofcrystal violet lactone and tetramethylbenzidine was added slowly to thisportion of the casein solution, with continued stirring, for about anhour. The portion of the casein solution containing the kaolin waspassed through a homogenizer, or other means for mixing and thoroughlydispersing the particles of kaolin in the casein solution, and the twoportions of casein solution, one containing the kaolin and the othercontaining the the crystal violet lactone and the tetramethylbenzidine,were then mixed thoroughly and applied as a coating to the base web ofpaper. This coating was then dried on the paper in the usual manner. Theresulting record material had a light bluish-white color approachingwhite.

It should be noted that the mixing of the ammoniacal kaolin-containingportion of the casein solution with the other portion of the caseinsolution, containingthe crystal violet lactone and thetetramethylbenzidine, results in an alkaline mixture, in which thecrystal violet lactone and the tetramethylbenzidine are precipitated inextremely fine particles.

In case gelatin is substituted for casein as the solid insulatin medium,the procedure described above is modified, in that the gelatin is firstdissolved in water at a temperature above 40 degrees centigrade, andthis gelatin solution is then divided into two equal parts, to one ofwhich the slurry of kaolin and water is added as before. The other partof the gelatin solution is made sufliciently ammoniacal to neutralizethe precipitate the crystal violet lactone and the tetramethylbenzidinewhen the hydrochloric acid solution of these ingredients is addedthereto. These two portions of the gelatin solution are then mixed, andthe mixture is applied as a coating to the paper and then dried. Itshould be noted that, when gelatin is used as the solid insulatingmedium, the gelatin solution should be kept at a temperature above 40degrees centigrade throughout the entire procedure.

In case methyl cellulose is used as the solid insulating medium insubstitution for the casein, a solution is prepared by dissolving about5 parts by Weight of methyl cellulose (of any viscosity between 2000 and4000 centipoises at 68 degrees Fahrenheit) in about 50 parts by weightof water, and this solution is divided into two equal parts. To oneportion of the methyl cellulose solution, the slurry of kaolin and wateris added, in the ratio of 40 parts by weight of kaolin to one part byweight of methyl cellulose, and mixed, as described in connection withthe use of casein. The other portion of the methyl cellulose solution isrendered sufiiciently ammoniacal to precipitate the crystal violetlactone and the tetramet'hylbenzidine from the hydrochloric acidsolution thereof, when the latter is added to and mixed with thisportion of the methyl cellulose solution in such proportions that theratio by weight of kaolin to crystal violet lacton andtetramethylbenzidine in the coating will be to 3. The two portions ofthe methyl cellulose solution are, then, thoroughly mixed and applied asa coating to the paper, which coating is dried.

actant so as to be an electron acceptor when in adsorption contact withsaid organic reactant. 7. The process of making a pressure-sensitiverecord material including the steps of forming a dispersion of solidparticles of a first colorforming reactant in a solution of a solidinsulating medium, derived from an organic filmforming hydrophiliccolloid substance, forming a dispersion of solid particles of a secondreactant 3,3 bis(p dimethylaminophenyl) 6 dimethylamino phthalide,having the stucture bUCHs):

in a solution of said insulating medium, mixing said dispersions,coating a base web with the mixture of said dispersions, and evaporatingthe solvent therefrom, leaving on the base web a coating of solidinsulating medium having said solid reactant particles interspersedtherethrough at random, the first reactant being an inorganic compoundupon which the second reactant is adsorbable, said first reactant beingso selected as to react in the absence of an ionizing medium to form adistinctive color when brought into adsorption contact with the secondreactant, and said inorganic reactant being in fine particle formproviding a large adsorbent surface area and which is an acid relativeto the second reactant so as to be an electron acceptor when inadsorption contact with said second reactant.

8. The process of making a pressure-sensitive record material includingthe steps of forming a dispersion of solid particles of a firstcolorforming reactant in a solution of a solid insulating medium,derived from an organic film-forming hydrophilic colloid substance,forming a dispersion of solid particles of a second co1or-forrningreactant which is a mixture of the compound 3,3 bis(pdimethylaminophenyl) 6 dimethylamino phthalide, having the structure andthe compound tetramethylbenzidine, having the structure in a solution ofsaid insulating medium, mixing said dispersions, coating a base web withthe mixture of said dispersions, and evaporating the solvent therefrom,leaving on the base Web a coating of solid insulating medium having saidsolid reactant particles interspersed therethrough at random, the firstreactant being an inorganic compound upon which the second reactant isadsorbable, said first reactant being so selected as to react with thesecond reactant, in the absence of an ionizing medium, to form adistinctive color when brought into adsorption contact with the secondreactant, and said first reactant being in fine particle form, providinga large adsorbent surface area, and which is an acid relative to thesecond reactant so as to be an electron acceptor when in adsorptioncontact with said second reactant.

9. The process of claim 8, in which the first color-forming reactant iskaolin.

10. The process of claim 9 in which the solid insulating medium iscasein.

11. The process of making a pressure-sensitive record material includingthe steps of forming a dispersion of solid particles of a firstcoloriorming reactant in a solution of a solid insulating medium,derived from an organic film-forming hydrophilic colloid substance,forming a dispersion of solid particles of a second color-iormingreactant in a solution of said insulating medium, said dispersion of thesolid particles of the second color-forming reactant being formed byprecipitation thereof, by the neutralization of an acidified solution ofsaid reactant in the insulating medium and said second color-formingreactant bein, a mixture of the compound 3,3 bis (p dimethylaminophenyl)6 dimethylamino phthalide, having the structure and the compoundtetramethylbenzidine, having the structure mixing said dispersions,coating a base Web with the mixture of said dispersions, and evaporatingthe solvent therefrom, leaving on the base web a coating of solidinsulating medium having said solid reactant particles interspersedtherethrough at random, the first one of said reactants being aninorganic compound selected so as to react in the absence of an ionizingmedium to form a distinctive color when brought into adsorption contactwith the second reactant compound, and the inorganic reactant being infine particle form and providing a large adsorbent surface area, andwhich is an acid relative to the second reactant so as to be an electronacceptor when in adsorption contact with said second reactant.

12. The process of claim 11 in which the inorganic color-formingreactant is kaolin.

13. The process of claim 12 in which the solid insulating medium iscasein.

BARRETT K. GREEN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,505,471 Green Apr. 25, 19502,505,481 Green Apr. 25, 1950

1. THE PROCESS OF MAKING A PRESSURE-SENSITIVE RECORD MATERIAL INCLUDINGTHE STEP OF FORMING ON A SUPPORTING MEMBER A FILM OF A SOLID INSULATINGMEDIUM, DERIVED FROM AN ORGANIC HYDROPHILIC COLLOID SUBSTANCE, HAVINGINTERSPERSED THERETHROUGH AT RANDOM SOLID PARTICLES OF A PLURALITY OFADSORPTION COLOR-FORMING REACTANTS, DISPOSED IN CONTIGUITY, BUTINSULATED FROM COLOR-FORMING REACTION CONTACT BY SUCH MEDIUM, AT LEASTONE OF SAID REACTANTS BEING KAOLIN AND AT LEAST ANOTHER OF SAID REATANTSBEING A MIXTURE OF THE COMPOUND 3,3 BIS(P-DIMETHYLAMINOPHENYL)-6-DIMETHYLAMINO PHTHALIDE, HAVING THE STRUCTURE